As one of plastic, information recording media in which information is written and read by focusing beams of a laser, etc., there is a so-called air sandwich-structured disk formed by adhering two disk substrates to each other through a spacer having a ring form.
And, a UV-curable adhesive, double-coated tape, ordinary-temperature curable adhesive and hot-melt adhesive are available as an adhesive for use in forming disks having such an air sandwich structure or another structure formed by adhering two disk substrates directly. In general, the UV-curable adhesive and double-coated tape have drawbacks of large deformation such as warpage, poor appearance such as cracks and pitting corrosion, and low adhesion strength. The double-coated tape also has a defect of including air between a recording medium layer and itself. The ordinary-temperature curable adhesive gives good appearance and has high adhesion strength. However, it involves a defect of large deformation, e.g. warpage.
On the other hand, the hot-melt adhesive applied by means of a roll coater, a nozzle, etc., gives good appearance and has high adhesion strength. Further, deformation such as warpage, caused by the hot-melt adhesive, is small as compared with the above adhesives, etc. Therefore, the hot-melt adhesive attracts attention as a promising one. However, when it is tested under high-temperature and high-humidity conditions (e.g. a temperature of 80.degree. C. and a humidity of 85%) for a long period of time (e.g. 300 hours), there are problems in that deviation occurs between two disks adhered to each other and large deformation such as warpage appears. In order to prevent the deviation and deformation, it is usual practice to use a hot-melt adhesive having a high melt-viscosity. In this case, however, the problem is that the hot-melt adhesive becomes too hard at room temperature and shows a decrease in adhesion power at a temperature lower than room temperature.